Catalyst, its preparation and use

ABSTRACT

A dehydrogenation catalyst is described that comprises an iron oxide, an alkali metal or compound thereof, and rhenium or a compound thereof. A process for preparing a dehydrogenation catalyst comprising preparing a mixture of iron oxide, an alkali metal or compound thereof, and rhenium or a compound thereof is also described. Additionally, a dehydrogenation process using the catalyst and a process for preparing polymers are described.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser. No. 60/915,808 filed May 3, 2007, the entire disclosure of which is herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a catalyst, a process for preparing the catalyst, and a process for the dehydrogenation of a dehydrogenatable hydrocarbon.

BACKGROUND

Dehydrogenation catalysts and the preparation of such catalysts are known in the art. Iron oxide based catalysts are customarily used in the dehydrogenation of dehydrogenatable hydrocarbons to yield, among other compounds, a corresponding dehydrogenated hydrocarbon. In this field of catalytic dehydrogenation of dehydrogenatable hydrocarbons to dehydrogenated hydrocarbons there are ongoing efforts to develop dehydrogenation catalysts that exhibit improved performance.

U.S. Pat. No. 6,191,065 describes a catalyst for the production of alkenylaromatics from alkylaromatics, wherein the catalyst is predominantly iron oxide, an alkali metal compound and less than about 300 ppm of a source for a noble metal, such as palladium, platinum, ruthenium, rhenium, osmium, rhodium or iridium. The amount of noble metal may be as much as 1000 ppm although the preferred amounts are lower. The patent teaches that when the noble metal is palladium, rhenium and rhodium, the amount is preferably less than 100 ppm, and most preferably less than 20 ppm. The catalyst may also comprise compounds based on cerium, molybdenum, tungsten and other such promoters.

SUMMARY OF THE INVENTION

The present invention provides a dehydrogenation catalyst comprising an iron oxide, an alkali metal or compound thereof, and rhenium or a compound thereof.

In a preferred embodiment, the invention provides a dehydrogenation catalyst comprising iron oxide, an alkali metal or compound thereof, and rhenium or a compound thereof wherein the rhenium or compound thereof is present in an amount of at least about 0.01 moles of rhenium per mole of iron oxide, calculated as Fe₂O₃.

The present invention provides a process for preparing a dehydrogenation catalyst comprising preparing a mixture of an iron oxide, an alkali metal or compound thereof, and rhenium or a compound thereof wherein the rhenium is present in an amount of at least about 0.01 moles of rhenium per mole of iron oxide, calculated as Fe₂O₃ and calcining the mixture.

The present invention also provides a process for preparing a dehydrogenation catalyst comprising preparing a mixture of iron oxide, an alkali metal or compound thereof, and a rhenium compound selected from the group consisting of rhenium dioxide, rhenium trioxide, rhenium(VII) oxide, and ammonium perrhenate and calcining the mixture.

The present invention further provides a process for dehydrogenating a dehydrogenatable hydrocarbon comprising contacting a feed comprising a dehydrogenatable hydrocarbon with a catalyst comprising an iron oxide, an alkali metal or compound thereof, and rhenium or a compound thereof.

The present invention still further provides a method of using a dehydrogenated hydrocarbon for making polymers or copolymers, comprising polymerizing the dehydrogenated hydrocarbon to form a polymer or copolymer comprising monomer units derived from the dehydrogenated hydrocarbon, wherein the dehydrogenated hydrocarbon has been prepared in a process for the dehydrogenation of a dehydrogenatable hydrocarbon as described above.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a catalyst that satisfies the need for improved dehydrogenation catalysts. The catalyst comprises an iron oxide, an alkali metal or compound thereof, and rhenium or a compound thereof. The catalyst comprising rhenium is more selective than a similar catalyst that does not contain rhenium. Additionally, a catalyst comprising rhenium and silver demonstrates improved performance over a similar catalyst that does not contain rhenium and silver.

The dehydrogenation catalyst is an iron oxide based catalyst. In addition, the iron may be present in the form of potassium ferrite or as a compound with any of the other catalyst components including rhenium. The catalyst comprises from 10 to 90 wt % iron oxide, calculated as Fe₂O₃. The catalyst preferably comprises from 40 to 85 wt % iron oxide, and more preferably comprises from 60 to 80 wt % iron oxide.

The iron oxide may be formed or processed by any process known to those skilled in the art. Additionally, the catalyst may comprise one or more types of iron oxide. The iron oxide may be formed by heat decomposition of iron halide to form iron oxide as described in U.S. Patent Application Publication 2003/0144566, which is hereinafter referred to as regenerator iron oxide. The regenerator iron oxide may optionally be treated to reduce the residual halide content in the iron oxide to at most 2000 ppm or preferably at most 1500 ppm. The iron oxide may be formed by spray roasting of iron chloride in the presence of Column Group 6 metals or hydrolyzable metal chlorides. In the alternative, the iron oxide may be formed by a precipitation process.

The iron oxide may be restructured before its use in the catalyst by the process described in U.S. Pat. No. 5,668,075 and U.S. Pat. No. 5,962,757. The iron oxide may be treated, washed or heat conditioned before its use in this catalyst as described in U.S. Pat. No. 5,401,485.

The iron oxide may be red, yellow, or black iron oxide. Yellow iron oxide is a hydrated iron oxide typically depicted as Fe₂O₃.H₂O or α-FeOOH. When yellow iron oxide is added, at least 5 wt %, or preferably at least 10 wt % of the total iron oxide in the catalyst, calculated as Fe₂O₃, may be yellow iron oxide, and at most 50 wt % of the total iron oxide may be yellow iron oxide. An example of a red iron oxide can be made by calcination of a yellow iron oxide made by the Penniman method. Iron oxide-providing compounds that may be present in the catalyst include goethite, hematite, magnetite, maghemite, and lepidocricite.

The alkali metal in the catalyst is selected from the group of alkali metals including lithium, sodium, potassium, rubidium, cesium and francium, and is preferably potassium. One or more of these metals may be used. The alkali metal may be present in the catalyst as a compound of an alkali metal. The alkali metals are generally present in a total quantity of at least 0.2 moles, preferably at least 0.25 moles, more preferably at least 0.45 moles, and most preferably at least 0.55 moles, per mole of iron oxide, calculated as Fe₂O₃. The alkali metals are generally present in a quantity of at most 5 moles, or preferably at most 1 mole, per mole of iron oxide. The alkali metal compound may include hydroxides; carbonates; bicarbonates; carboxylates, for example, formates, acetates, oxalates and citrates; nitrates; and oxides. The preferred alkali metal compound is potassium carbonate.

The rhenium may be present as any compound of rhenium, and is preferably rhenium oxide. The rhenium may be added as any compound of rhenium, rhenium powder or rhenium nanoparticles. The rhenium is preferably added as rhenium dioxide, rhenium trioxide, rhenium(VII) oxide or ammonium perrhenate. The rhenium is generally present in a total quantity of at least 0.01 moles, preferably at least 0.025 moles and more preferably at least 0.045 moles, and most preferably at least 0.05 moles per mole of iron oxide calculated as Fe₂O₃. The rhenium is generally present in a total quantity of at most 1 mole, and preferably at most 0.5 moles per mole of iron oxide.

The catalyst may further comprise a lanthanide. The lanthanide is selected from the group of lanthanides of atomic number in the range of from 57 to 66 inclusive. The lanthanide is preferably cerium. The lanthanide may be present as a compound of a lanthanide. The lanthanide is generally present in a total quantity of at least 0.02 moles, preferably at least 0.05 moles, more preferably at least 0.06 moles per mole of iron oxide, calculated as Fe₂O₃. The lanthanide is generally present in a total quantity of at most 0.2 moles, preferably at most 0.15 moles, more preferably at most 0.14 moles per mole of iron oxide. The lanthanide compound may include hydroxides; carbonates; bicarbonates; carboxylates, for example, formates, acetates, oxalates and citrates; nitrates; and oxides. The preferred lanthanide compound is cerium carbonate.

The catalyst may further comprise an alkaline earth metal or compound thereof. The alkaline earth metal may be calcium or magnesium, and it is preferably calcium. The alkaline earth metal compound is generally present in a quantity of at least 0.01 moles, and preferably at least 0.02 moles per mole of iron oxide calculated as Fe₂O₃. The alkaline earth metal compound is generally present in a quantity of at most 1 mole, and preferably at most 0.2 moles per mole of iron oxide.

The catalyst may further comprise a Group 6 metal or compound thereof. The Group 6 metal may be molybdenum or tungsten, and it is preferably molybdenum. The Group 6 metal is generally present in a quantity of at least 0.01 moles, preferably at least 0.02 moles per mole of iron oxide, calculated as Fe203. The Group 6 metal is generally present in a quantity of at most 0.5 moles, preferably at most 0.1 moles per mole of iron oxide.

The catalyst may further comprise silver or a compound thereof. The silver may be present as silver, silver oxide, or silver ferrite. The silver is preferably added to the catalyst mixture as silver oxide, silver chromate, silver ferrite, silver nitrate, or silver carbonate.

Additional catalyst components that may be combined with the iron oxide include metals and compounds thereof selected from the group consisting of: Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mn, Tc, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Au, Zn, Cd, Hg, Al, Ga, In, Tl, Si, Ge, Sn, Pb, P, As, Sb, Bi, S, Se and Te. These components may be added by any method known to those skilled in the art. The additional catalyst components may include hydroxides; bicarbonates; carbonates; carboxylates, for example formates, acetates, oxalates and citrates; nitrates; and oxides. Palladium, platinum, ruthenium, rhodium, iridium, copper, and chromium are preferred additional catalyst components.

The catalyst may be prepared by any method known to those skilled in the art. For example, a paste may be formed comprising iron oxide, alkali metal or a compound thereof, rhenium or a compound thereof and any additional catalyst component(s). A mixture of these catalyst components may be mulled and/or kneaded or a homogenous or heterogeneous solution of any of these components may be impregnated on the iron oxide. Sufficient quantities of each component may be calculated from the composition of the catalyst to be prepared. Examples of applicable methods can be found in U.S. Pat. Nos. 5,668,075; 5,962,757; 5,689,023; 5,171,914; 5,190,906, 6,191,065, and EP 1027928, which are herein incorporated by reference.

In forming the catalyst, a mixture comprising iron oxide, alkali metal or a compound thereof, rhenium or a compound thereof and any additional catalyst component(s) may be shaped into pellets of any suitable form, for example, tablets, spheres, pills, saddles, trilobes, twisted trilobes, tetralobes, rings, stars, hollow and solid cylinders, and asymmetrically lobed particles as described in U.S. Patent Application Publication 2005-0232853. The addition of a suitable quantity of water, for example up to 30 wt %, typically from 2 to 20 wt %, calculated on the weight of the mixture, may facilitate the shaping into pellets. If water is added, it may be at least partly removed prior to calcination. Suitable shaping methods are pelletizing, extrusion, and pressing. Instead of pelletizing, extrusion or pressing, the mixture may be sprayed or spray-dried to form a catalyst. If desired, spray drying may be extended to include pelletization and calcination.

An additional compound may be combined with the mixture that acts as an aid to the process of shaping and/or extruding the catalyst, for example a saturated or unsaturated fatty acid (such as palmitic acid, stearic acid, or oleic acid) or a salt thereof, a polysaccharide derived acid or a salt thereof, or graphite, starch, or cellulose. Any salt of a fatty acid or polysaccharide derived acid may be applied, for example an ammonium salt or a salt of any metal mentioned hereinbefore. The fatty acid may comprise in its molecular structure from 6 to 30 carbon atoms (inclusive), preferably from 10 to 25 carbon atoms (inclusive). When a fatty acid or polysaccharide derived acid is used, it may combine with a metal salt applied in preparing the catalyst, to form a salt of the fatty acid or polysaccharide derived acid. A suitable quantity of the additional compound is, for example, up to 1 wt %, in particular 0.001 to 0.5 wt %, relative to the weight of the mixture.

After formation, the catalyst mixture may be dried and calcined. Drying generally comprises heating the catalyst at a temperature of from about 30° C. to about 500° C., preferably from about 100° C. to about 300° C. Drying times are generally from about 2 minutes to 5 hours, preferably from about 5 minutes to about 1 hour. Calcination generally comprises heating the catalyst, typically in an inert, for example nitrogen or helium or an oxidizing atmosphere, for example an oxygen containing gas, air, oxygen enriched air or an oxygen/inert gas mixture. The calcination temperature is typically at least about 600° C., or preferably at least about 700° C., more preferably at least 825° C. The calcination temperature will typically be at most about 1600° C., or preferably at most about 1300° C. Typically, the duration of calcination is from 5 minutes to 12 hours, more typically from 10 minutes to 6 hours.

The catalyst formed according to the invention may exhibit a wide range of physical properties. The surface structure of the catalyst, typically in terms of pore volume, median pore diameter and surface area, may be chosen within wide limits. The surface structure of the catalyst may be influenced by the selection of the temperature and time of calcination, and by the application of an extrusion aid.

Suitably, the pore volume of the catalyst is at least 0.01 ml/g, more suitably at least 0.05 ml/g. Suitably, the pore volume of the catalyst is at most 0.5, preferably at most 0.4 ml/g, more preferably at most 0.3 ml/g, and most preferably at most 0.2 ml/g. Suitably, the median pore diameter of the catalyst is at least 500 Å, in particular at least 1000 Å. Suitably, the median pore diameter of the catalyst is at most 20000 Å, in particular at most 15000 ∪. In a preferred embodiment, the median pore diameter is in the range of from 2000 to 10000 Å. As used herein, the pore volumes and median pore diameters are as measured by mercury intrusion according to ASTM D4282-92, to an absolute pressure of 6000 psia (4.2×10⁷ Pa) using a Micromeretics Autopore 9420 model; (130° contact angle, mercury with a surface tension of 0.473 N/m). As used herein, median pore diameter is defined as the pore diameter at which 50% of the mercury intrusion volume is reached.

The surface area of the catalyst is preferably in the range of from 0.01 to 20 m²/g, more preferably from 0.1 to 10 m²/g.

The crush strength of the catalyst is suitably at least 10 N/mm, and more suitably it is in the range of from 20 to 100 N/mm, for example about 55 or 60 N/mm.

In another aspect, the present invention provides a process for the dehydrogenation of a dehydrogenatable hydrocarbon by contacting a dehydrogenatable hydrocarbon and steam with an iron oxide based catalyst made according to the invention to produce the corresponding dehydrogenated hydrocarbon.

The dehydrogenated hydrocarbon formed by the dehydrogenation process is a compound having the general formula: R¹R²C═CH₂ wherein R¹ and R² independently represent an alkyl, alkenyl or a phenyl group or a hydrogen atom.

The dehydrogenatable hydrocarbon is a compound having the general formula: R¹R²HC—CH₃ wherein R¹ and R² independently represent an alkyl, alkenyl or a phenyl group or a hydrogen atom.

A suitable phenyl group may have one or more methyl groups as substitutes. A suitable alkyl group generally has from 2 to 20 carbon atoms per molecule, and preferably from 3 to 8 carbon atoms such as in the case of n-butane and 2-methylbutane. Suitable alkyl substituents are propyl (—CH₂—CH₂—CH₃), 2-propyl (i.e., 1-methylethyl, —CH(—CH₃)₂), butyl (—CH₂—CH₂—CH₂—CH₃), 2-methyl-propyl (—CH₂—CH(—CH₃)₂), and hexyl (—CH₂—CH₂—CH₂—CH₂—CH₂—CH₃), in particular ethyl (—CH₂—CH₃). A suitable alkenyl group generally has from about 4 to about 20 carbon atoms per molecule, and preferably from 4 to 8 carbon atoms per molecule.

The dehydrogenatable hydrocarbon may be an alkyl substituted benzene, although other aromatic compounds may be applied as well, such as alkyl substituted naphthalene, anthracene, or pyridine. Examples of suitable dehydrogenatable hydrocarbons are butyl-benzene, hexylbenzene, (2-methylpropyl)benzene, (1-methylethyl)benzene (i.e., cumene), 1-ethyl-2-methyl-benzene, 1,4-diethylbenzene, ethylbenzene, 1-butene, 2-methylbutane and 3-methyl-1-butene. It is possible to convert n-butane with the present process via 1-butene into 1,3-butadiene and 2-methylbutane via tertiary amylenes into isoprene.

Examples of preferred dehydrogenated hydrocarbons that can be produced by the process are butadiene, alpha methyl styrene, divinylbenzene, isoprene and styrene.

The dehydrogenation process is frequently a gas phase process; wherein a gaseous feed comprising the reactants is contacted with the solid catalyst. The catalyst may be present in the form of a fluidized bed of catalyst particles or in the form of a packed bed. The process may be carried out as a batch process or as a continuous process. Hydrogen may be a further product of the dehydrogenation process, and the dehydrogenation in question may be a non-oxidative dehydrogenation. Examples of applicable methods for carrying out the dehydrogenation process can be found in U.S. Pat. Nos. 5,689,023; 5,171,914; 5,190,906; 6,191,065, and EP 1027928, which are herein incorporated by reference.

It is advantageous to apply water, which may be in the form of steam, as an additional component of the feed. The presence of water will decrease the rate of deposition of coke on the catalyst during the dehydrogenation process. Typically the molar ratio of water to the dehydrogenatable hydrocarbon in the feed is in the range of from 1 to 50, more typically from 3 to 30, for example from 5 to 10.

The dehydrogenation process is typically carried out at a temperature in the range of from 500 to 700° C., more typically from 550 to 650° C., for example 600° C., or 630° C. In one embodiment, the dehydrogenation process is carried out isothermally. In other embodiments, the dehydrogenation process is carried out in an adiabatic manner, in which case the temperatures mentioned are reactor inlet temperatures, and as the dehydrogenation progresses the temperature may decrease typically by up to 150° C., more typically by from 10 to 120° C. The absolute pressure is typically in the range of from 10 to 300 kPa, more typically from 20 to 200 kPa, for example 50 kPa, or 120 kPa.

If desired, one, two, or more reactors, for example three or four, may be applied. The reactors may be operated in series or parallel. They may or may not be operated independently from each other, and each reactor may be operated under the same conditions or under different conditions.

When operating the dehydrogenation process as a gas phase process using a packed bed reactor, the LHSV may preferably be in the range of from 0.01 to 10 h⁻¹, more preferably in the range of from 0.1 to 2 h⁻¹. As used herein, the term “LHSV” means the Liquid Hourly Space Velocity, which is defined as the liquid volumetric flow rate of the hydrocarbon feed, measured at normal conditions (i.e., 0° C. and 1 bar absolute), divided by the volume of the catalyst bed, or by the total volume of the catalyst beds if there are two or more catalyst beds.

The conditions of the dehydrogenation process may be selected such that the conversion of the dehydrogenatable hydrocarbon is in the range of from 20 to 100 mole %, preferably from 30 to 80 mole %, or more preferably from 35 to 75 mole %.

The activity (T70) of the catalyst is defined as the temperature under given operating conditions at which the conversion of the dehydrogenatable hydrocarbon in a dehydrogenation process is 70 mole %. A more active catalyst thus has a lower T70 than a less active catalyst. The corresponding selectivity (S70) is defined as the selectivity to the desired product at the temperature at which conversion is 70 mole %.

The dehydrogenated hydrocarbon may be recovered from the product of the dehydrogenation process by any known means. For example, the dehydrogenation process may include fractional distillation or reactive distillation. If desirable, the dehydrogenation process may include a hydrogenation step in which at least a portion of the product is subjected to hydrogenation by which at least a portion of any byproducts formed during dehydrogenation, are converted into the dehydrogenated hydrocarbon. The portion of the product subjected to hydrogenation may be a portion of the product that is enriched in the byproducts. Such hydrogenation is known in the art. For example, the methods known from U.S. Pat. Nos. 5,504,268; 5,156,816; and U.S. Pat. No. 4,822,936, which are incorporated herein by reference, are readily applicable to the present invention.

One preferred embodiment of a dehydrogenation process is the nonoxidative dehydrogenation of ethylbenzene to form styrene. This embodiment generally comprises feeding a feed comprising ethylbenzene and steam to a reaction zone containing catalyst at a temperature of from about 500° C. to about 700° C. Steam is generally present in the feed at a steam to hydrocarbon molar ratio of from about 7 to about 15. In the alternative this process may be carried out at a lower steam to hydrocarbon molar ratio of from about 1 to about 7, preferably of from about 2 to about 6.

Another preferred embodiment of a dehydrogenation process is the oxidative dehydrogenation of ethylbenzene to form styrene. This embodiment generally comprises feeding ethylbenzene and an oxidant, for example, oxygen, iodide, sulfur, sulfur dioxide, or carbon dioxide to a reaction zone containing catalyst at a temperature of from about 500° C. to about 800° C. The oxidative dehydrogenation reaction is exothermic so the reaction can be carried out at lower temperatures and/or lower steam to oil ratios.

Another preferred embodiment of a dehydrogenation process is the dehydrogenation of isoamylenes to form isoprene. This embodiment generally comprises feeding a mixed isoamylene feed comprising 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene into a reaction zone containing catalyst at a temperature of from about 525° C. to about 675° C. The process is typically conducted at atmospheric pressure. Steam is generally added to the feed at a steam to hydrocarbon molar ratio of from about 13.5 to about 31.

Another preferred embodiment of a dehydrogenation process is the dehydrogenation of butene to form butadiene. This embodiment generally comprises feeding a mixed butylenes feed comprising 1-butene and 2-butene (cis and/or trans isomers) to a reaction zone containing catalyst at a temperature of from about 500° C. to about 700° C.

Due to the endothermic nature of most of these dehydrogenation processes, additional heat input is often desirable to maintain the required temperatures to maintain conversion and selectivity. The heat can be added before a reaction zone, between reaction zones when there are two or more zones, or directly to the reaction zone.

A preferred embodiment of a suitable heating method is the use of a conventional heat exchanger. The process stream may be heated before entering the first or any subsequent reactors. Preferred sources of heat include steam and other heated process streams.

Another preferred embodiment of a suitable heating method is the use of a flameless distributed combustion heater system as described in U.S. Pat. No. 7,025,940, which is herein incorporated by reference.

Another preferred embodiment of a suitable heating method is catalytic or noncatalytic oxidative reheat. Embodiments of this type of heating method are described in U.S. Pat. Nos. 4,914,249; 4,812,597; and U.S. Pat. No. 4,717,779; which are herein incorporated by reference.

The dehydrogenated hydrocarbon produced by the dehydrogenation process may be used as a monomer in polymerization processes and copolymerization processes. For example, the styrene obtained may be used in the production of polystyrene and styrene/diene rubbers. The improved catalyst performance achieved by this invention with a lower cost catalyst leads to a more attractive process for the production of the dehydrogenated hydrocarbon and consequently to a more attractive process which comprises producing the dehydrogenated hydrocarbon and the subsequent use of the dehydrogenated hydrocarbon in the manufacture of polymers and copolymers which comprise monomer units of the dehydrogenated hydrocarbon. For applicable polymerization catalysts, polymerization processes, polymer processing methods and uses of the resulting polymers, reference is made to H. F. Marks, et al. (ed.), “Encyclopedia of Polymer Science and Engineering”, 2^(nd) Edition, New York, Volume 16, pp 1-246, and the references cited therein.

The following examples are presented to illustrate the invention, but they should not be construed as limiting the scope of the invention. Examples 1-7 and Examples 11-15 were conducted in cooperation with hte Aktiengesellschaft, Heidelberg, Germany. The other examples were conducted using standard isothermal testing conditions.

Example 1 (Comparative)

A catalyst was prepared by combining: 13.5 g iron oxide (Fe₂O₃) made by heat decomposition of iron chloride, 1.5 g yellow iron oxide (FeOOH), 3.97 g potassium carbonate, 2.07 g cerium carbonate (as hydrated Ce₂(CO₃)₃ containing 52 wt % Ce), 0.24 g molybdenum trioxide, and 0.24 g calcium carbonate. Water was added to the mixture and the mixture was mulled for 15 minutes. This mixture was extruded to pellets that were 3 mm in diameter and about 3 mm in length. The pellets were dried in air at 170° C. for 15 minutes and subsequently calcined in air at 900° C. for 1 hour. The pellets were crushed with a mortar and pestle and sieved with an appropriate sieve such that the particle size was between 315-500 μm.

A 1.1 ml sample of the catalyst was loaded into the isothermal zone of a multiwell reactor (5 mm inner diameter) and was used for the preparation of styrene from ethylbenzene. Inert was loaded above and below the catalyst bed. The testing conditions were as follows: outlet partial pressure 76 kPa, steam to ethylbenzene molar ratio 10, and LHSV 0.65 h⁻¹. In this test, the temperature was initially held at 590° C. for a period of about 13 days. The catalyst was then tested for 24 hours at each of three different temperatures: about 590° C., about 595° C., and about 600° C. The conversion of ethylbenzene (“C”) and selectivity to styrene (“S”) at the three temperatures, as measured, is shown in Table 1. This catalyst was tested in duplicate and the data shown is the average results.

Examples 2-7

Catalysts were prepared according to the invention. The ingredients described in Example 1 were used. The catalysts of examples 2-7 contained rhenium that was added in different forms and amounts (millimoles of Re per mole of iron oxide, calculated as Fe₂O₃) as shown in Table 1. The catalysts were tested under the same conditions as the catalyst of Example 1, and the catalyst performance is shown in Table 1.

TABLE 1 Rhenium First Temperature Second Temperature Third Temperature Example Compound Amount T ° C. C % S % T ° C. C % S % T ° C. C % S % 1 (Comp) N/A 0 590 65.6 96.3 595 68.9 95.9 600 72.1 95.6 2 ReO₂ 15 589 59.1 97.3 595 62.8 96.9 600 66.3 96.8 3 ReO₃ 15 589 60.4 96.9 594 64.2 96.6 599 67.6 96.3 4 Re₂O₇ 15 590 64.2 96.6 595 68.1 96.3 601 71.3 95.9 5 Re₂O₇ 50 590 63.2 96.8 596 67.2 96.4 601 70.6 96.1 6 Re₂O₇ 150 590 43.4 97.0 595 49.6 97.1 600 60.5 97.1 7 NH₄ReO₄ 15 590 61.4 96.9 595 65.4 96.6 601 69.1 96.3

As can be seen from Examples 1-7, a catalyst containing rhenium is more selective than a catalyst without rhenium.

Examples 8-10 (Comparative)

Catalysts were prepared by combining: 900 g iron oxide (Fe₂O₃) (made by heat decomposition of iron chloride) that contained 0.08 wt % Cl and had a surface area of 3.2 m²/g and 100 g yellow iron oxide (FeOOH) with sufficient potassium carbonate, cerium carbonate (as hydrated Ce₂(CO₃)₃ containing 52 wt % Ce), molybdenum trioxide, and calcium carbonate to give a catalyst with a composition as shown in Table 2. Water (about 10 wt %, relative to the weight of the dry mixture) was added to form a paste, and the paste was extruded to form 3 mm diameter cylinders that were then cut into 6 mm lengths. The pellets were dried in air at 170° C. for 15 minutes and subsequently calcined in air at 900° C. for 1 hour. The composition of the catalyst after calcination is shown in Table 2 as millimoles per mole of iron oxide, calculated as Fe₂O₃. The catalysts of Examples 9 and 10 also contained rhenium as shown in Table 2.

A 100 cm³ sample of each catalyst was used for the preparation of styrene from ethylbenzene under isothermal testing conditions in a reactor designed for continuous operation. The conditions were as follows: absolute pressure 76 kPa, steam to ethylbenzene molar ratio 10, and LHSV 0.65 h⁻¹. In this test, the temperature was initially held at 595° C. for a period of about 10 days. The temperature was later adjusted such that a 70 mole % conversion of ethylbenzene was achieved (T70). The selectivity (S70) to styrene at the selected temperature was measured.

TABLE 2 Composition, millimoles/mole of iron oxide T70 S70 Example Re Mo Ce Ca K ° C. % 8 (Comp) 0 18 80 25 620 596.1 95.6 9 (Comp) 1.1 (added as 18 80 25 620 597.7 95.6 Re₂O₇) 10 (Comp)  7.5 (added as 18 80 25 620 595.6 95.4 NH₄ReO₄)

As can be seen from Examples 8-10, small amounts of rhenium added to a catalyst do not improve the selectivity of the catalyst.

Examples 11 (Comparative) and 12-15

Examples 11-15 demonstrate the effects on catalyst performance of adding rhenium and silver to catalysts. These Examples also demonstrate the effects of changes in calcination temperature and cerium levels. These catalysts were prepared according to the method of Examples 1 except for the differences in ingredients and the differences in calcination temperature, as shown in Table 3. Rhenium was added as Re₂O₇ and silver was added as Ag₂O. The catalysts were tested under the same conditions as the catalyst of Example 1 except that the catalyst was broken in for 21 days and the conversion and selectivity were measured at about 590° C., about 593° C., and about 596° C. The respective temperatures, conversion (“C”) and selectivity to styrene (“S”) are shown in Table 4.

TABLE 3 Calc. Example K Mo Ca Ce Re Ag T ° C. 11 (Comp) 620 18 25 80 0 0 900 12 620 18 25 120 25 200 825 13 620 18 25 120 25 60 975 14 620 18 25 80 62.5 130 900 15 620 18 25 120 100 60 825

TABLE 4 First Second Third Temperature Temperature Temperature Example T ° C. C % S % T ° C. C % S % T ° C. C % S % 11 (Comp) 591 66.3 96.5 594 68.2 96.3 597 70.2 96.1 12 590 70.3 96.1 593 71.8 95.7 596 73.5 95.4 13 590 64.3 97.1 593 66.2 96.9 596 68.3 96.8 14 590 66.3 96.9 593 67.9 96.8 596 69.8 96.6 15 589 69.3 96.4 592 67.9 96.8 595 72.5 96.0

One skilled in the art can vary many of the variables shown above in addition to other variables to achieve a dehydrogenation catalyst that is most effective for a particular application. Additional catalyst components may also be added to affect the properties and performance of the catalyst. The catalyst manufacturing process may be altered with respect to such variables as drying times and temperatures, calcination times and temperatures, and processing speed to affect the properties and performance of the catalyst. 

1. A dehydrogenation catalyst comprising an iron oxide, an alkali metal or compound thereof, and rhenium or a compound thereof wherein the rhenium or compound thereof is present in an amount of about 0.01 moles to 0.5 moles of rhenium per mole of iron oxide, calculated as Fe₂O₃.
 2. The catalyst of claim 1 wherein the rhenium or compound thereof is present in an amount of from about 0.02 to about 0.5 moles of rhenium per mole of iron oxide, calculated as Fe₂O₃.
 3. The catalyst of claim 1 wherein the rhenium or compound thereof is present in an amount of at most 0.3 moles of rhenium per mole of iron oxide, calculated as Fe₂O₃.
 4. The catalyst of claim 1 wherein the rhenium or compound thereof is present in an amount of from about 0.04 to about 0.25 moles of rhenium per mole of iron oxide, calculated as Fe₂O₃.
 5. The catalyst of claim 1 wherein the alkali metal or compound thereof comprises potassium.
 6. The catalyst of claim 1 further comprising a lanthanide or a compound thereof.
 7. The catalyst of claim 6 wherein the lanthanide or compound thereof comprises cerium.
 8. The catalyst of claim 1 further comprising an alkaline earth metal or compound thereof.
 9. The catalyst of claim 8 wherein the alkaline earth metal or compound thereof comprises calcium.
 10. The catalyst of claim 1 further comprising a Group 6 metal or compound thereof.
 11. The catalyst of claim 10 wherein the Group 6 metal or compound thereof comprises molybdenum.
 12. The catalyst of claim 1 further comprising silver or a compound thereof.
 13. The catalyst of claim 1 further comprising a metal selected from the group consisting of palladium, platinum, ruthenium, osmium, rhodium, iridium, titanium and copper.
 14. The catalyst of claim 1 wherein the iron oxide comprises regenerator iron oxide formed by the heat decomposition of an iron halide.
 15. The catalyst of claim 1 wherein the iron oxide is restructured by heat-treating in the presence of a restructuring agent.
 16. A process for preparing a dehydrogenation catalyst comprising preparing a mixture of an iron oxide, an alkali metal or compound thereof, and rhenium or a compound thereof, wherein the rhenium is present in an amount of at least about 0.01 moles to 0.5 moles of rhenium per mole of iron oxide, calculated as Fe₂O₃, and calcining the mixture.
 17. The process of claim 16 further comprising adding an alkaline earth metal or compound thereof to the mixture.
 18. The process of claim 16 further comprising adding a Group 6 metal or compound thereof to the mixture.
 19. The process of claim 16 wherein the calcining is carried out at a temperature of from about 600° C. to about 1300° C.
 20. The process of claim 16 wherein the calcining is carried out at a temperature of from about 750° C. to about 1200° C.
 21. The process of claim 16 wherein the calcining is carried out at a temperature greater than 800° C.
 22. A process for preparing a dehydrogenation catalyst comprising preparing a mixture of iron oxide, an alkali metal or compound thereof, and a rhenium compound selected from the group consisting of rhenium dioxide, rhenium trioxide, rhenium(VII) oxide, and ammonium perrhenate and calcining the mixture, wherein the rhenium compound is present in an amount of about 0.01 moles to 0.5 moles of rhenium per mole of iron oxide, calculated as Fe₂O₃. 